Time division multiplexed (TDM) digital PBX telephone systems have not only enhanced voice communication, but have also expanded the utility of a building's installed telephone wiring for performing other functions. In a TDM PBX system, analog-to-digital (and digital-to-analog) conversion occurs in the telephone handset with individual handset codecs. As a result the digital PBX requires only a fraction of the real time required by analog systems and, therefore, is capable of multiplexing data channel information in with the voice channel bit stream.
Typically the PBX provides information exchange between the switch matrix and each system handset through a combined 8 KBPS data channel, a 64 KBPS voice channel, and an 8 KBPS order wire channel. The data channel allows the PBX to provide signal control over unrelated building equipment. This is a control function which would otherwise be impractical due to building rewiring costs. U.S. Pat. No. 4,551,832, of common assignee herewith, discloses one such PBX based control system used to provide central control of HVAC equipment in hotels.
With the advent of desk top computers there have been major capital expenditures by corporations in purchasing workstation equipment, such as word processing equipment and personal computers. This equipment is both expensive and portable. There are prior art security devices, such as cables which secure the equipment in its location, i.e. passive restraint type devices. However, with wide dissemination of the equipment at remote sites throughout company offices, it is desirable to provide some type of automatic theft security.